KEY POINTS

  • Astronomers observed a calcium-rich supernova in X-ray for the first time ever
  • Calcium-rich supernovas are so rare that their true nature is elusive to scientists
  • The very first X-ray observations shed light into the nature of such rare events

Astronomers examined a calcium-rich supernova using X-rays for the first time ever. 

It was in 2019 when amateur astronomer Joel Shepherd spotted a bright orange burst while he was observing the Messier 100 spiral galaxy 55 million light years from Earth. He immediately reported the findings to the global astronomical community, which then turned their telescopes to the supernova event.

The community responded to the report so quickly that the supernova, dubbed SN 2019ehk, was observed just 10 hours after the explosion. Leading observatories in the U.S. such as NASA's Swift Satellite and the W.M. Keck Observatory in Hawaii were used for the study. It was using the Swift Satellite that the study co-author Daichi Hiramatsu, of the University of California, Santa Barbara, observed the supernova event in X-ray, something that wasn't done before.

"In the world of transients, we have to discover things very, very fast before they fade. Initially, no one was looking for X-rays. Daichi noticed something and alerted us to the strange appearance of what looked like X-rays," senior author Raffaella Margutti of Northwestern University said in a news release. "We looked at the images and realized something was there. It was much more luminous than anybody would have ever thought. There were no preexisting theories that predicted calcium-rich transients would be so luminous in X-ray wavelengths."

The researchers believe that the star, likely a compact one, released an outer layer of gas during its last days. When it exploded, its material collided with the gas, emitting the bright burst of X-ray that they observed and powering the chemical process that creates calcium.

Supernova Image: Artist's interpretation of SN 2019ehk. The purple gas emitted before the explosion created calcium-rich material. Photo: Aaron M. Geller/Northwestern University

Observations using Keck also found that SN 2019ehk produced the most calcium ever observed in a single event. The calcium that stars emit when they die is the same calcium found in our bones and teeth. The calcium from calcium-rich supernova explosion accounts for up to half of the calcium in the Universe.

"Most massive stars create small amounts of calcium during their lifetimes, but events like SN 2019ehk appear to be responsible for producing vast quantities of calcium and in the process of exploding disperse it through interstellar space within galaxies," study co-author Régis Cartier of NOIRLab said in a news release. "Ultimately this calcium makes its way into forming planetary systems and into our bodies in the case of our Earth!"

Such calcium-rich supernova events are considered so rare that it is hard for scientists to study them. To observe one, especially using X-ray imaging, will provide a truly unique glimpse into the event.

"These events are so few in number that we have never known what produced calcium-rich supernova," study lead Wynn Jacobson-Galan of Northwestern University said. "By observing what this star did in its final month before it reached its critical, tumultuous end, we peered into a place previously unexplored, opening new avenues of study within transient science."

The study, which was authored by nearly 70 co-authors from 15 countries, is published in The Astrophysical Journal.